This invention relates to new boron resins possessing very high selective absorbent power which are stable in organic solvents and in aqueous acid and alkaline solutions.
More particularly, the invention relates to boron resins consisting of an acrylic polymer matrix functionalized with quaternary ammonium groups, an epoxy group and phenylboric groups, of general formula (I): ##STR2## in which P is a polyacrylic matrix,
R is --(CH.sub.2).sub.n -- where n lies between 0 and 5, PA1 R.sub.1 and R.sub.2, which can be the same or different, are C.sub.1 -C.sub.5 alkyl, PA1 R.sub.3 is --(C.sub.n H.sub.2n) where n varies from 1 to 5, PA1 R.sub.4 is H or C.sub.1 -C.sub.5 alkyl, PA1 X.sup.- is an anion chosen from halogens and hydroxyl;
The invention also relates to a process for producing the resins defined by general formula (I).
In European Patent 85102934.8 we have already described boron resins With a polyacrylic matrix bifunctionalized with quaternary ammonium groups and alkylphenylboric groups, which possess good chemical and mechanical stability characteristics and can be used in industrial processes, they having a marked selective absorbent action particularly in separating lactulos from its mixtures with other carbohydrates, generally lactose and galactose.
It has now been discovered that boron resins with further improved selectivity in separating sugars can be obtained by the process of the present invention, which is described in detail hereinafter.
The boron resins of the present invention are prepared from a polyacrylic resin obtained by cross-linking an acrylic ester with divinylbenzene and preferably having the following characteristics:
______________________________________ Percentage of cross-linkage 4% Mean pore diameter 1100 .ANG. Specific surface area 10 m.sup.2 /g Particle size 0.2-0.4 mm (90%) ______________________________________
This resin is firstly subjected to a transamination reaction by reacting with disubstituted diamines by known methods.
Separately, a particular boroxin of the type corresponding to the indicated formula is obtained by reacting an aminophenylboroxin of formula ##STR3## with hydroxybenzaldehyde, to produce an intermediate of formula (II) ##STR4## To produce the boron resin, either:
(1) the transaminated polyacrylic resin is firstly reacted with an epihalohydrin: ##STR5## and the product of this reaction reacted with the boroxin (II): ##STR6## to give ##STR7## and then ##STR8## or:
(2) the boroxin (II) is firstly reacted with the epihalohydrin and the product of this reaction reacted with the transaminated polyacrylic resin, the product of this latter reaction then being reduced by NaBH.sub.4 in methanol, to obtain a product of formula (I): ##STR9##
The preferred conditions for implementing the individual steps of the process in the form of the two alternatives described schematically heretofore are as follows:
(a) Transamination of the polyacrylic matrix: this is conducted by known methods U.S. Pat. No. 4,506,036, reacting the polyacrylic matrix with a disubstituted diamine.
(b) Preparation of the boroxin of formula (II): a substituted benzeneboronic acid such as an aminobenzeneboronic or oxybenzeneboronic acid is mixed with p-oxybenzaldehyde in an alcoholic solvent, and left at ambient temperature for 15-24 hours. The crude product can be used for the subsequent reactions after filtration.
(c) Reaction of the transaminated polyacrylic resin with an epihalohydrin: the aminated acrylic resin is pretreated by a process comprising regeneration in Cl form by reaction with a dilute NaCl and HCl solution at about ambient temperature, washing with demineralized water until neutral, regeneration in OH form by treatment in aqueous ammonia at around ambient temperature, washing with demineralized water until neutral, washing with acetone and drying under vacuum.
At this point the resin is placed in a polar aprotic solvent such as dioxane, and heated under reflux with epichlorohydrin dissolved in the same solvent, triggering the reaction with potassium iodide and heating under reflux between 40 and 100 C for 15-25 hours. After filtration and repeated washes with the same solvent, the crude product is ready for the subsequent reactions.
(d) Reaction of the product obtained in (c) with the boroxin of formula (II) followed by reduction: this process is conducted by suspending the product obtained in (c) in a polar aprotic solvent such as dioxane, then adding the product obtained in (b). The suspension is kept at ambient temperature for 15-30 hours under agitation. It is filtered and the product taken up in alcohol. The suspension is treated with NaBH.sub.4 for 8-12 hours at a temperature of about 10-20 C.
After filtration, the resin is washed repeatedly by kneading with ethanol and with a mixture of ethanol and dilute hydrochloric acid, and finally with dilute hydrochloric acid alone.
(e) Reaction of the boroxin of formula (II) with the epihalohydrin: the crude product obtained in (b) is dissolved in the epihalohydrin and the mixture heated at 30-50 C for 15-24 hours. The excess epihalohydrin is then distilled off at reduced pressure at a temperature not exceeding 50 C.
The residue is taken up in alcohol and left under agitation under cold conditions for some hours.
The mixture is filtered under reduced pressure to recover the required product.
(f) Reaction of the product obtained in (e) with the aminated acrylic resin followed by reduction: the aminated acrylic resin, pretreated as described in (c) above, is placed in a solvent of the type used in (d), such as dioxane, a product such as that obtained in (e) is added, the reaction triggered with potassium iodide and the mixture heated under reflux at a temperature of between 40 and 80 C for 15-25 hours.
It is then filtered through a Buchner funnel and the residue obtained is taken up in alcohol. It is then reduced with NaBH.sub.4 and purification as indicated for the step described in (d) above.
Some practical embodiments of the processes and resin of the present invention are given hereinafter in order to make the processes and resin more easily reproducible.